Current communication systems, for example digital cellular communications systems, utilize certain capabilities in mobile stations to aid in communication handoff of the mobile station from one communication channel to another. This technique is called mobile assisted handoff, or MAHO. During MAHO, a mobile station is instructed by its serving base-station (or the mobile station knows in advance) to measure transmissions made by adjacent base-stations to determine the quality of those transmissions relative to the transmission of the serving base-station. The mobile station then reports the measured quality of those transmissions to the serving base-station where a handoff evaluation is performed. If any adjacent base-station provides a better quality transmission than does the serving base-station, a communication handoff of the subscriber unit is initiated. While the above describes MAHO implemented in a cell-to-cell handoff from the serving base-station to an adjacent base-station, MAHO can be equally implemented in a sector-to-sector handoff within a given cell.
In current digital cellular communications systems, MAHO is implemented by monitoring a control channel assigned to each sector/cell of the system, where each control channel is at a particular frequency. However, since each sector/cell of the system has its own control channel at a particular frequency, a large number of talk channels, or voice channels, are wasted since potential frequencies that could be used for voice channels are utilized as control channels specifically for the implementation of MAHO.
Implementation of MAHO by monitoring control channels has other disadvantages. Typically, a mobile station making a MAHO measurement makes a power measurement (RSSI) on a control channel. However, these sequences are short for control channels, thus a mobile station is required to make several measurements (for example, over several timeslots of a time division multiple access (TDMA) digital cellular communications system) to obtain accurate measurements. Consequently, a mobile station may, in some instances, lose communication with its serving base-station before an accurate MAHO measurement can be obtained.
Thus a need exists for a communication system which provides MAHO capability without wasting potential traffic channels and losing communication during handoff.